1. Field of the Invention
The present invention relates to a die clamping apparatus having a toggle type clamping mechanism applied to a molding machine such as a die casting machine or an injection molding machine.
Also, the present invention relates to a die clamping force measurement method in a die clamping apparatus capable of correctly measuring the die clamping force.
Further, the present invention relates to a die clamping force adjusting method of a die clamping apparatus capable of correctly adjusting the die clamping force.
2. Description of the Related Art
In the die clamping apparatus of for example a die casting machine, a die clamping force of a pair of dies compatible with the injection pressure of molten metal at the time of injection is required. The die clamping apparatuses are roughly classified into direct pressure type die clamping apparatuses directly pressing against a movable die and toggle type die clamping apparatuses pressing against the same via a toggle mechanism.
In a toggle type die clamping apparatus, there is a self lock mechanism of the toggle mechanism, so there are various advantages such as saving of energy in comparison with a direct pressure type die clamping apparatus.
Here, an example of the configuration of a toggle type die clamping apparatus will be explained by referring to FIG. 1 to FIG. 4.
FIG. 1 is a longitudinal sectional view of the configuration of a toggle type die clamping apparatus. The upper half from the center line CL shows the state before the start of closing the die, while the lower half shows the state of completion of closing of the die. Further, FIG. 2 is a side view of the die clamping apparatus shown in FIG. 1.
In FIG. 1 and FIG. 2, a die clamping apparatus 200 is provided with a pair of dies 4 comprising a fixed die 4b and a movable die 4a, a link housing 1, a fixed die plate 2 with the fixed die 4b attached thereto, a movable die plate 3 with the movable die 4a attached thereto, a base 5, a toggle mechanism 6, a crosshead 7, a hydraulic cylinder 8, a piston rod 9, a guide rod 10, and tie bars 11.
The die clamping apparatus 200 is provided with an upper and lower pair of toggle mechanisms 6 comprising three links 6a, 6b, and 6c between the movable die plate 3 and the link housing 1.
The fixed die plate 2 is fixed to the base 5, and the link housing 1 and the movable die plate 3 are provided movably on the base 5.
The link housing 1 and the movable die plate 3 are connected by tie bars 11 as shown in FIG. 2. Usually, four tie bars 11 are provided.
The link 6c of the toggle mechanism 6 is pivotally connected to the crosshead 7, the hydraulic cylinder 8 is mounted at substantially the center portion of an outer end face of the link housing 1, and a front end of the piston rod 9 of this hydraulic cylinder 8 is connected to the crosshead 7.
The crosshead 7 is movably guided to the guide rod 10. This crosshead 7 moves along the guide rod 10 in accordance with the movement of the piston rod 9.
As shown in FIG. 2, when the piston rod 9 of the hydraulic cylinder 8 is advanced from a state where the links 6a, 6b, and 6c of the toggle mechanism 6 are folded and the links 6a, 6b, and 6c are extended, the movable die plate 3 moves toward the fixed die plate 2 and, as shown in FIG. 3, the movable die 4a contacts the fixed die 4b. In the state shown in FIG. 3, the links 6a, 6b, and 6c of the toggle mechanism 6 are not completely extended, and no die clamping force is generated between the movable die 4a and the fixed die 4b. Further, a distance H0 between the movable die plate 3 and the fixed die plate 2 in the state where the movable die 4a and the fixed die 4b contact and the die clamping force has not been generated between them is referred to as the die height.
When the piston rod 9 is further advanced from this state, the links 6a, 6b, and 6c of the toggle mechanism 6 become in almost straight alignment as shown in FIG. 4 and self lock. Further, by the extension of the toggle mechanism 6, the tie bars 11 connecting the link housing 1 and the fixed die plate 2 are stretched due to elastic deformation, a die clamping force in accordance with the amount of deformation of the tie bars 11 is generated between the movable die 4a and the fixed die 4b, and the link housing 1 moves on the base 5 with an amount of movement in accordance with the amount of deformation of the tie bars 11.
When the die height H0 is changed by the adjustment of the die clamping force or by a change of the die 4 in the die clamping apparatus 200 of the above configuration, the position relative to the fixed die plate 2 is adjusted by the link housing 1.
As the position adjustment device for adjusting the position of the link housing 1, for example a spur gear type position adjustment device or a chain type or worm gear type position adjustment device are known. Such a position adjustment device is built in the link housing 1. The position adjustment device basically is comprised of tie bar nuts screwed with the four tie bars 11. By controlling the rotation of these tie bar nuts in synchronization, the link housing 1 can be moved along the tie bars 11.
In the measurement of the die clamping force in the toggle type die clamping apparatus 200 having the above configuration, as disclosed in for example Japanese Examined Patent Publication (Kokoku) No. 5-74770, the method of embedding electric load meters in ends of the tie bars 11 at the link housing 1 side, directly detecting the amounts of deformation of the tie bars 11 at the time of clamping by the electric type load meters, and finding the die clamping force based on the amounts of deformation was employed.
With this method, however, there were the disadvantages that the cost of the electric load meters was high, the work for attachment of the electric load meters was troublesome, the cost of manufacture rose, maintenance of the detection precision was difficult, etc.
In order to overcome such disadvantages, a method of not directly measuring the amounts of deformation of the tie bars 11, but detecting the amount of movement of the link housing 1 relative to the base 5 when it shifts from a die open state as shown in FIG. 1 to a die closed state shown in FIG. 4 and calculating the die clamping force based on this amount of movement is disclosed in for example Japanese Examined Patent Publication (Kokoku) No. 5-36219. Namely, the die clamping force is calculated by regarding the amount of movement of the link housing 1 when it shifts from the die open state to the die closed state as the amount of deformation of the tie bars 11.
However, the position adjustment device is interposed between the link housing 1 and the tie bars 11. If mechanical error such as backlash exists between the tie bars 11 and the tie bar nuts screwed to them in this position adjustment device, the amount of the mechanical error is contained in the detected amount of movement of the link housing 1, so the amount of movement of the link housing 1 when it shifts from the die open state to the die closed state and the amounts of deformation of the tie bars 11 may not correctly coincide. For this reason, in the above method, the correct measurement of the die clamping force was difficult. Particularly, it was easily influenced by the backlash between the tie bar and the tie bar nut after adjusting the position of the link housing 1 by the position adjustment device so as to adjust the die clamping force and change the die height H0 by the change of the dies 4, so the die clamping force could not be correctly measured.
An object of the present invention is to provide a die clamping apparatus capable of correctly measuring a die clamping force without use of sensors such as load meters for directly detecting the amounts of deformation of the tie bars in the die clamping apparatus.
Another object of the present invention is to provide a die clamping apparatus capable of correctly and automatically adjusting the die clamping force.
Still another object of the present invention is to provide a method of measurement of die clamping force capable of correctly measuring the die clamping force without use of sensors such as load meters for directly detecting the amounts of deformation of the tie bars.
Still another object of the present invention is to provide a method of adjustment of die clamping force capable of correctly adjusting the die clamping force.
According to a first aspect of the present invention, there is provided a die clamping apparatus comprising a fixed die plate fixed on a base and holding a fixed die, a movable die plate for holding a movable die facing the fixed die and movable on the base, a link housing connected with the fixed die plate by tie bars while interposing the movable die plate therebetween and movable on the base, a toggle mechanism for generating a die clamping force between the movable die plate and the fixed die plate through the tie bars by moving apart the movable die plate and the link housing, a position adjusting means provided between the link housing and the tie bars and connecting the link housing and the tie bars so as to enable the position adjustment of the link housing to the tie bars, a link housing position detecting means for detecting a first position of the link housing on the base in a state where the movable die moves from a predetermined die open position to a die closing direction and a die clamping force has not been generated and a second position of the link housing on the base in a state where the clamping is completed, and a die clamping force calculating means for calculating the die clamping force based on a difference of the first and second positions detected by the link housing position detecting means.
Preferably, the die clamping apparatus further comprises a die clamping force adjusting means for calculating an amount of compensation for compensating the position of the link housing to the tie bars so that the die clamping force becomes a reference die clamping force based on a difference between the calculated die clamping force calculated by the die clamping force calculating means and the reference die clamping force set in advance and outputting the same to the position adjusting means.
According to a second aspect of the present invention, there is provided a die clamping force measurement method in a die clamping apparatus provided with a fixed die plate fixed on a base and holding a fixed die, a movable die plate for holding a movable die facing the fixed die and movable on the base, a link housing connected with the fixed die plate by tie bars while interposing the movable die plate therebetween and movable on the base, a toggle mechanism for generating a die clamping force between the movable die plate and the fixed die plate through the tie bars by moving apart the movable die plate and the link housing, and a position adjusting means provided between the link housing and the tie bars and connecting the related link housing and the tie bars so as to enable the position adjustment of the link housing to the tie bars, comprising steps of moving the movable die plate from the predetermined open position toward the fixed die plate by operating the toggle mechanism, detecting a first position of the link housing on the base in a state where the movable die plate moved and a die clamping force has not been generated, detecting a second position of the link housing on the base in a state where the clamping is completed, calculating an amount of movement of the link housing from the detected first and second positions of the link housing, and calculating the die clamping force based on the calculated amount of movement.
According to a third aspect of the present invention, there is provided a die clamping force adjusting method in a die clamping apparatus provided with a fixed die plate fixed on a base and holding a fixed die, a movable die plate for holding a movable die facing the fixed die and movable on the base, a link housing connected with the fixed die plate by tie bars while interposing the movable die plate therebetween and movable on the base, a toggle mechanism for generating a die clamping force between the movable die plate and the fixed die plate through the tie bars by moving apart the movable die plate and the link housing, and a position adjusting means provided between the link housing and the tie bars and connecting the link housing and the tie bars so as to enable the position adjustment of the link housing to the tie bars, comprising steps of moving the movable die plate from a predetermined open position toward the fixed die plate by operating the toggle mechanism, detecting a first position of the link housing on the base in a state where the movable die plate moved and a die clamping force has not been generated, detecting a second position of the link housing on the base in a state where the clamping is completed, calculating an amount of movement of the link housing from the detected first and second positions of the link housing, calculating the die clamping force based on the calculated amount of movement, calculating an amount of compensation for compensating the position of the link housing relative to the tie bar so that the die clamping force becomes a reference die clamping force based on a difference between the calculated die clamping force and the reference die clamping force set in advance, and outputting the same to the position adjusting means.
In the present invention, the movable die plate located at the predetermined die open position is moved toward the fixed die by operating the toggle mechanism. When the movable die plate moves, a reaction force from the toggle mechanism acts upon the link housing. This reaction force acting upon the link housing acts also upon the tie bars connected to the link housing through the position adjusting means.
At this time, if for example mechanical error such as backlash exists between nut members provided in the position adjusting means and the tie bars screwed therewith, this mechanical error will be eliminated by the reaction force acting upon the link housing.
Then, the first position of the link housing in the state where the backlash is eliminated as described above is detected.
Further, when the movable die and the fixed die are clamped, the tie bars extend by the elastic deformation, and the link housing moves in a direction moving apart from the movable die plate.
The second position of the link housing in the state where the die clamping is completed is detected.
The die clamping force calculating means calculates the die clamping force based on the difference of the first and second positions detected as described above, that is, the amount of movement of the link housing. The mechanical error existing in the position adjusting means is not contained in the amount of movement of this link housing, so the calculated die clamping force becomes the correct value.
Further, in the present invention, the amount of correction for correcting the position of the link housing so that the die clamping force becomes the reference die clamping force is calculated from the difference between the die clamping force calculated as described above and the die clamping force set in advance, then the position of the link housing is adjusted by the position adjusting means. At this time, the die clamping force calculated as described above is the correct value, so the position of the link housing is adjusted with a high precision.